OSU demystifies how oat fungus kills plants

CORVALLIS, Ore. – Researchers at Oregon State University may have discovered why some grains are susceptible to a yield-reducing fungus.

They've mapped out the battle that takes place inside a cell when the fungus Cochliobolus victoriaeinfects Arabidopsis thaliana, a small plant in the mustard family that's used as a research model. They suspect that a similar process occurs in oats, barley, rice, beans and Brachypodium grasses because they are believed to share a similar gene.

Their findings, published today in the online version of the journal Science, could eventually help plant breeders develop varieties of grains and beans that resist certain diseases, said Tom Wolpert, an OSU plant pathologist and co-author of the paper, "Tricking the Guard: Exploiting Plant Defense for Disease Susceptibility."

Wolpert and others at OSU discovered that victorin, a toxin produced by the fungus, attacks Arabidopsis by binding to a protein called TRX-h5. This protein, however, has a guard watching over it called LOV1. When something tries to mess with the protein, the guard causes the cells to "commit suicide" in defense.

"The plant is doing what it thinks it should do and is turning on a defense," Wolpert said.

That strategy works for the plant when it's fighting fungi that need their hosts to be living cells in order to survive. Such fungi are called biotrophs and collect nutrients from the living cells. What the plant doesn't know, however, it that Cochliobolus victoriae is a type of fungus called a necrotroph that feeds on dead cells instead.

"The fungus is tricking the plant to kill its cells so it can eat them," said OSU plant pathologist Jennifer Lorang, the lead author of the study.

Cochliobolus victoriae causes a disease called Victoria blight, which in the 1940s severely reduced U.S. yields of oats that were descended from a variety named Victoria. The fungus damages leaves, kills seedlings, causes seeds to ripen prematurely, and weakens stems so that the plant falls over.

A gene called Vb in the Victoria-type oats made them susceptible to the fungus, but that same gene is believed to protect them from another fungus called crown rust. Cochliobolus victoriae is no longer a problem in oats because new varieties have been developed that don't have the Vb gene.

Last year, U.S. farmers produced $2.6 billion of rice, $827 million of dry, edible beans, $822 million of barley and $186 million of oats, according to the U.S. Department of Agriculture.

Jennifer Lorang and Tom Wolpert examine oats growing in a greenhouse at Oregon State University. The OSU plant pathologists have figured out how a fungus that infects oats tricks plant cells into committing suicide. Photo by Tiffany Woods.